Power actuated fastener tool

ABSTRACT

A power actuated tool for driving a fastener into a work surface includes a firing pin for firing an explosive charge to drive the fastener. The firing pin is held in a cocked position against a spring bias by a rotary sear which is displaced rearwardly during cocking by pressing a barrel against the work surface. In the cocked condition, the sear is aligned with a trigger mechanism which can be actuated to pivot the sear and thereby cause release of the firing pin which is then driven by the spring bias to fire the charge.

BACKGROUND OF THE INVENTION

The present invention relates to power actuated fastener tools.

Power actuated tools for driving a fastener such as a nail, into asubstrate, such as a concrete beam, conventionally comprise a barrelfrom which the fastener is expelled by means of a piston driven bydetonation of an explosive charge. The charge is fired by release of afiring pin after cocking of the tool. In conventional firing mechanismsthe firing pin has a slot of sufficient depth to allow a pawl to becontained within the slot. A spring inside the slot biases the pawl toproject out of the slot to engage with, and be retained by, a cockingpiece. To cock the tool, the forward end of the barrel is pressed hardagainst the work surface and this results in the rear face of the barrelpushing against the cocking piece which retracts the firing pin againstthe bias of a firing pin spring. When the firing pin is in the cockedposition, a sear which is connected to the trigger is aligned with thepawl. When the trigger is actuated, the sear retracts the pawl into thefiring pin, thus releasing the firing pin from the cocking piece wherebythe firing pin is driven by the firing pin spring towards the explosivecharge to fire the power actuated tool.

The firing pin is of relatively small diameter and the space availablefor mounting the pawl within the firing pin is limited. For the tool toperform consistantly the fit between the pawl and the slot in the firingpin must be maintained. It has been found that repeated firing resultsin the pawl wearing against both the cocking piece and the slot wall.This results in the pawl becoming loose within the cocking piece andfiring pin. Consequently when the sear applies the upward force uponactuation of the trigger, instead of driving the pawl upward into theslot of the firing pin, the pawl may twist and jam. Thus a greaterrelease force is required which makes actuation of the triggerincreasingly difficult. It has also been known for a pawl to jam andthen to suddenly, and unexpectedly, release, thus firing the tool, whichcan be very dangerous.

SUMMARY OF THE INVENTION

According to the present invention, there is provided a power actuatedtool for driving a fastener into a substrate, comprising a firingmechanism including a firing pin for firing an explosive charge to drivethe fastener from a barrel of the tool, spring means for driving thefiring pin, and a rotary sear pivotal between a position in which thesear engages an abutment surface of the pin whereby to entrain the pinand a released position in which the sear is released from the abutmentsurface whereby to permit driving of the firing pin towards the chargeunder the bias of the spring means.

DESCRIPTION OF THE PREFERRED EMBODIMENT

An embodiment of the invention will now be described, by way of exampleonly, with reference to the accompanying drawings, in which:

FIG. 1 is a sectional view of a power actuated tool fitted with a firingmechanism in accordance with the present invention, the tool being shownin its cocked condition.

FIG. 2 is a fragmentary schematic view of a firing pin, rotary sear andtrigger sear plate in the cocked condition.

FIG. 3 is a view similar to FIG. 2, but after firing;

FIG. 4 is a fragmentary schematic view on line 4--4 of FIG. 1 andshowing the firing pin, rotary sear, and sear plate in the cockedposition; and

FIG. 5 is a view similar to FIG. 4, but after firing.

The power actuated tool 1 comprises a barrel 3 mounted in a receiverassembly 5, and a firing mechanism 7 having a firing pin 9 mounted inthe receiver assembly rearwardly of the barrel 3. The barrel 3 houses apiston (not shown) which is actuated by an explosive charge mounted in acharge chamber 11 at the rear of the barrel 3, to drive a fastenerwithin the forward end of the barrel 3 into a substrate such as a beam.The barrel 3 is mounted for axial movement within the receiver assembly5 and after firing can be moved forwardly of the receiver assembly 5 inorder to reset the piston into the rear end of the barrel 3 inpreparation for the next firing. Prior to the next firing, a freshcharge is inserted into the charge chamber 11 (either manually orautomatically) and the barrel 3 together with the piston is withdrawninto the receiver assembly 5. In order to fire the tool, the forward endof the barrel 3 is pressed against the work surface which has the effectof moving the barrel 3 back further into the receiver assembly 5 whichcauses cocking of the firing mechanism 7.

The firing pin 9 of the firing mechanism 7 is stepped to provide aforwardly facing abutment face 13. The firing pin 9 is biased in anaxially forwards direction by means of a compression spring 15. Thefiring pin 9 is associated with a rotary sear 17 which is mounted to oneside of the firing pin 9 for rectilinear movement parallel to the axisof the firing pin 9 and also for rotation about the axis of rectilinearmovement. The sear 17 comprises, at its rear end, a radial lug 19 whichco-operates with the firing pin 9 to hold the pin 9 in its cockedposition, as will be described. A compression spring 21 acts to apply anaxially forwards bias to the rotary sear 17 and is also fixed to boththe receiver assembly 5 and the sear 17 so as to apply a torsional biasto the sear 17 in a sense to pivot the lug 19 into engagement with thefiring pin 9. The rotary sear 17 is fixedly mounted at the rear end of acocking rod 23 so that the sear 17 and cocking rod 23 are movable as aunit. A radial lug 25 at the forward end of the cocking rod 23 co-actswith a sear plate 27 of a trigger mechanism 29 in the cocked position,as will be described. The trigger mechanism 29 includes a trigger 31.

In the condition in which the barrel 3 has been withdrawn into thereceiver assembly 5 after re-setting of the piston and prior to cocking,the rotary sear 17 is forwardly of the abutment face 13 of the firingpin 9 with the lug 19 being biased towards the firing pin 9 by thetorsional bias of the spring 21. The lug 25 at the forward end of thecocking rod 23 is also forwardly of the trigger sear plate 27 in thiscondition. Upon pushing the forward end of the barrel 3 against the worksurface in order to cock the tool, the barrel 3 moves back further intothe receiver assembly 5. A stepped abutment surface 33 at the rear endof the barrel 3 engages the forward end of the cocking rod 23 and causesthe cocking rod and rotary sear 17 to be displaced rearwardly with thebarrel 3 against the bias of the spring 21. During this movement, thelug 19 on the rotary sear 17 engages the forward abutment face 13 on thefiring pin 9 and causes retraction of the firing pin 9 against the biasof the compression spring 15. When the barrel 3 is retracted to itsmaximum extent within the receiver assembly 5, the rear end of thebarrel 3 including the charge chamber 11 is firmly against the forwardface of the rear part of the receiver assembly 5 housing the firingmechanism 7, and the lug 25 at the forward end of the cocking rod 23 isaligned with the sear plate 27 of the trigger 31. Actuation of thetrigger 31 causes linear displacement of the sear plate 27 which engagesthe lug 25 and pivots the lug 25 and thus the cocking rod 23 and rotarysear 17 in a sense to move the lug 19 angularly away from the firing pin9, to thereby release the firing pin 9 which is then driven against thecharge in the charge chamber 11 under the bias of the compression spring15.

After firing, the barrel 3 is moved forwardly to reset the piston. Theforwards movement of the barrel 3 permits the rotary sear 17 and cockingrod 23 to move forwardly under the bias of the spring 21 whereby the lug19 on the rotary sear 17 moves along the larger diameter rear portion 37of the firing pin 9 until it reaches the stepped abutment face 13 atwhich point the torsional bias of the spring 21 causes the lug 19 topivot inwardly across the abutment face 13 in preparation for the nextfiring.

In the embodiment described, to facilitate mounting within the receiverassembly 5, the rotary sear 17 and cocking rod 23 are installedseparately and are then locked together to form a unit by means of aconnecting pin. In an alternative construction it would, however, bepossible to produce the rotary sear 17 and cocking rod 23 as an integralunit which is installed as a whole into the receiver assembly 5. Inanother alternative construction, the components are installedseparately and come into that working relation only during the cockingstroke.

The firing mechanism 7 described is advantageous because there are nocomponents of the release mechanism with the firing pin 9 so thedifficulties of mounting the components within the small diameter firingpin 9 and of maintaining the fit between the firing pin 9 and releasecomponents are avoided. The firing mechanism 7 also provides a verysmooth firing action. This is due to the relatively small angle ofrotation of the rotary sear 17. The rotation is typically 20° during thefiring operation and this results in only a small increase in thetorsional force component of the compression spring 21. Accordingly amuch smoother searing action is provided. The compression spring 21 isrelatively long so that it can easily handle this small degree ofrotation without jamming.

In addition the firing mechanism 7 is wear-compensating as any wear ofthe lug 19 against the stepped abutment face 13 will automatically betaken up by the spring bias applied to the firing pin 9 by the firingpin spring.

The embodiment has been described by way of example only andmodifications are possible within the scope of the invention.

I claim:
 1. A power actuated tool for driving a fastener into asubstrate, comprising a firing mechanism including a firing pin movablealong a predetermined axis of movement for firing an explosive charge todrive the fastener from a barrel of the tool, spring means for drivingthe firing pin, and a rotary sear pivotable between a position in whichthe sear engages an abutment surface of the pin whereby to entrain thepin and a released position in which the sear is released from theabutment surface whereby to permit driving of the firing pin along saidaxis towards the charge under the bias of the spring means, wherein thesear is pivotable about an axis parallel to the axis of movement of thefiring pin, the sear is movable in a direction parallel to the axis ofmovement of the firing pin so as to entrain the pin by engagement withthe abutment surface in order to cock the firing mechanism, the barrelis displaceable within a body of the tool, and cocking of the firingmechanism is effected by pressing a front end of the barrel against awork surface to cause relative rearward displacement of the barrel inrelation to the body, the sear being displaced rearwardly by therearward displacement of the barrel to thereby cause rearwarddisplacement of the firing pin against the bias of the spring means withthe firing pin being entrained by the sear.
 2. A tool according to claim1 wherein the sear is mounted for rotation with an actuating member, andin the cocked condition of the firing mechanism, the actuating member isaligned with a trigger mechanism such that actuation of the triggermechanism pivots the actuating member and thereby the sear into itsreleased position.
 3. A tool according to claim 2, wherein the sear ismounted at a rear end portion of a cocking rod and the actuating memberis mounted at a front end position of the cocking rod, the cocking rodis parallel to the axis of the firing pin, the cocking rod is rotatableto provide the rotation of the sear, and the cocking rod is axiallydisplaceable, and wherein the trigger mechanism includes a sear plate,the actuating member of the sear being movable into alignment with thesear plate when the cocking rod is moved rearwardly on cocking, andactuation of a trigger of the trigger mechanism causing engagement ofthe sear plate with the actuating member whereby to pivot the sear intoits released position.
 4. A tool according to claim 3, comprisingtorsion spring means biasing the sear into its engaged position.
 5. Atool according to claim 4, wherein the torsion spring means comprises acompression spring which applies a torsional bias to the sear and alsoapplies a forwards axial bias to the sear.
 6. A tool according to claim3, wherein the sear is in the form of a lug extending radially of thepivotal axis of the cocking pin to engage the abutment surface of thefiring pin.
 7. A tool according to claim 3, wherein the abutment surfaceof the firing pin is defined by a forward face formed on a step in thefiring pin.